Re: [Vala] Is there a way to use the Vala coroutines to achieve the same effect as in the following Python snippet (coroutines returning partial results in an iterator-like way) ?

[Serge Hulne <serge hulne gmail com>]

In the meantime, tried the "scanner" example (my last entry in the Vala
maling list with an iterator.

Of course, since the vala iterator returns one item at a time it does the
trick.

The problem, on the second degree is that the vala iterator needs know in
advance the value of the next element t be reutuned (via get) and does not
wait.

An obvious way around this is to store the words (continuously pulled from
the input stream) temporary in a Queue, and to "feed to the Queue" on one
hand (scan method), and to "consume from the Queue" on the other hand (get()
method), hence using a sort of temporary dynamic buffer (and preserving the
order of the data).

Pb with this alternative scheme:

- Writing to a Vala Queue is O(1).
- reading (and deleting) from it is O(log(n))

So this alternative sheme, while emulating a "generator" and hence, saving a
lot of memory (compared to returning all the elements at once, as a list),
is extremely slow (many orders of magnitude).

Perhaps there are other alternatives:

- Sockets (probably too slow and overkill).
- Threads ?
All suggestions welcome !

Sincerely,
Serge Hulne.


Ref. : Hereunder : The scanner case-study (with the naive list-based
implementation)

//////////////////
using Posix;
using Gee;


LinkedList<string> scanner(string fname) {

    var f = FileStream.open(fname, "r");

    if (f==null) {
        Posix.stdout.printf("File missing !\n");
        exit(1);
    }

    StringBuilder wordBuffer = new StringBuilder("");
    char c = ' ';
    int wordBuffer_length = 0;
    var erased = true;
    var wordList = new LinkedList<string>();

    while (!f.eof()) {
        c = (char) f.getc();
        //if (!isalnum(c))
        if (isspace(c)) {
            if (wordBuffer.len>0) {
                //Posix.stdout.printf("word = %s\n", wordBuffer.str);
                wordList.add(wordBuffer.str);
                if (erased == false) {
                    wordBuffer.erase(0,-1);
                    wordBuffer_length = 0;
                    erased = true;
                }
            }
        } else {
            wordBuffer_length++;
            //Posix.stdout.printf("%d\n", wordBuffer_length);
            wordBuffer.append_c(c);
            erased = false;
        }
    }

    return wordList;
}



void main(string[] args) {
    var fname = "../corpora/shakes.txt";

    // -- testing scanner --

    var list = scanner(fname);
    var i = 0;
    foreach (var item in list) {
        stdout.printf("%s\n", item);
        i++;
        if (i > 10) return;
    }

}
/////////////////


On Sat, Jul 9, 2011 at 8:39 AM, Luca Bruno <lethalman88 gmail com> wrote:

> On Sat, Jul 09, 2011 at 08:04:38AM +0800, Nor Jaidi Tuah wrote:
> > > "The yield statement is only used when defining a generator function,
> and is
> > > only used in the body of the generator function. Using a yield
> statement in
> > > a function definition is sufficient to cause that definition to create
> a
> > > generator function instead of a normal function."
> >
> > I use such feature before in Ruby and miss it in Vala.
> > So, I'm anxiously awaiting the answer to the following question
> > in the original post.
>
> Vala has no generators and this behavior has nothing to do with coroutines.
> So I guess it's useless to show a possible solution without syntax
> support, you would say "it's not the same".
>
> --
> http://www.debian.org - The Universal Operating System